javascript顺序数组简单实现个二分查找

  function bsearch(A,x){
        //l：查找范围左 r:查找范围右
        let l = 0, //查询范围左边界
            r = A.length-1, //查找范围右边界
            guess //中间猜测位置
        while(l <= r){
            //guess等于l,r中间位置
            guess = Math.floor( (l+r)/2 )       

            //判断当前位置是否为要查找的值，是则返回下标
            if(A[guess] === x) return guess
            //如果当前位置值大于要查询的值 右边界位置减一
            else if(A[guess] > x) r = guess -1
            //否则左边界位置加1
            else l = guess + 1
        }
        //找不到返回-1
        return -1
    }
    const a = [3,5,4,7,12,42,47,66,71,78];
    console.log(bsearch(a,12))//4
    console.log(bsearch(a,4))//-1
    console.log(bsearch(a,66))//7
    console.log(bsearch(a,5))//1